Antioxidant mixture for low viscous polyalkylene glycol basestock

ABSTRACT

The invention relates to a lubricant comprising a polyalkylene glycol basestock, an aromatic amine of the formula (I) as defined hereinafter, and a thioether of the formula (II) as defined hereinafter. The invention further relates to a method for preparing the lubricant comprising the step of contacting the polyalkylene glycol basestock, the aromatic amine of the formula (I), and the thioether of the formula (II); and to a method for reducing the oxidative degradation of the lubricant comprising the step of contacting the polyalkylene glycol basestock, the aromatic amine of the formula (I), and the thioether of the formula (II).

The invention relates to a lubricant comprising a polyalkylene glycol basestock, an aromatic amine of the formula (I) as defined hereinafter, and a thioether of the formula (II) as defined hereinafter. The invention further relates to a method for preparing the lubricant comprising the step of contacting the polyalkylene glycol basestock, the aromatic amine of the formula (I), and the thioether of the formula (II); and to a method for reducing the oxidative degradation of the lubricant comprising the step of contacting the polyalkylene glycol basestock, the aromatic amine of the formula (I), and the thioether of the formula (II). Combinations of preferred embodiments with other preferred embodiments are within the scope of the present invention.

Lubricants with polyalkylene glycol basestock tend to degradation upon prolonged heating.

Object was to find antioxidants to reduce the degradation of polyalkylene glycol basestock at high temperatures.

The object was solved by a lubricant comprising a polyalkylene glycol basestock,

an aromatic amine of the formula (I)

wherein R1 and R2 are H or together represent the group A

and R3 and R4 are independently H or C₂-C₃₀ alkyl,

and a thioether of the formula (II)

The object was also solved by a method for preparing the lubricant comprising the step of contacting the polyalkylene glycol basestock, the thioether of the formula (II), and the aromatic amine of the formula (I).

The object was also solved by a method for reducing the oxidative degradation of the polyalkylene glycol basestock comprising the step of contacting the polyalkylene glycol basestock, the thioether of the formula (II), and the aromatic amine of the formula (I).

The polyalkylene glycol basestock is usually an alkoxylated alcohol, preferably an ethoxylated and propoxylated C₁-C₂₀ alkanol or C₂-C₂₀ alkandiol, in particular an ethoxylated and propoxylated C₁-C₈ alkanol.

Suitable alkoxylated alcohols are ethoxylated, ethoxylated and propoxylated, or ethoxylated and butoxylated. Preferably, alkoxylated alcohols are ethoxylated and propoxylated.

The alkoxylated alcohols may have a number average molecular weight Mn in the range from 400 to 10 000 Da, preferably from 700 to 3000 Da, and in particular from 1000 to 1500 Da. The Mn may be calculated based on the hydroxy number.

The alkoxylated alcohol may contain 20 to 80 wt % ethylene oxide units, and 80 to 20 wt % of propylene oxide units. The alkoxylated alcohol preferably contains 30 to 70 wt % ethylene oxide units, and 70 to 30 wt % of propylene oxide units. In particular, the alkoxylated alcohol contains 40 to 60 wt % ethylene oxide units, and 60 to 40 wt % of propylene oxide units. The wt % of the ethylene oxide and propylene oxide usually sum up to 100 wt % The alkoxy groups in the alkoxylated alcohol may be random or in block sequence. Preferably the alkoxy groups (e.g. the ethoxy and propoxy groups) in the alkoxylated alcohol are random sequence.

The polyalkoxylate chain of the alkoxylated (e.g. ethoxylated and propoxylated) alcohols may be terminated by a hydroxy group or a C₁ to C₄ alkyl, wherein the hydroxy group is preferred.

Suitable alcohol units in the alkoxylated alcohol are linear or branched C₁-C₂₀ alkanol or C₂-C₂₀ alkandiol, preferably C₁-C₂₀ alkanol or C₂-C₈ alkandiol, and in particular C₁-C₆ alkanol or C₂-C₆ alkandiol.

In another preferred form the alcohol units in the alkoxylated (e.g. ethoxylated and propoxylated) alcohol are linear or branched C₁-C₁₂ alkanol, preferably C₁-C₆ alkanol, and in particular C₁-C₄ alkanol.

The alcohol units in the alkoxylated alcohol may be a technical mixture of various chain lengths and isomers.

The polyalkylene glycol basestock may have a kinematic viscosity at 40° C. in the range from 10-300 mm²/s, preferably from 20-150 mm²/s, and in particular from 35-80 mm²/s.

The polyalkylene glycol basestock may have a kinematic viscosity at 100° C. in the range from 3-80 mm²/s, preferably from 5-40 mm²/s, and in particular from 8-20 mm²/s.

The kinematic viscosity may be determined according to ASTM D 445.

The polyalkylene glycol basestock may be water soluble (e.g. at 20° C.), such as at least 10 g/l, preferably at least 100 g/l.

The lubricant may comprise at least 50 wt %, preferably at least 70 wt %, and in particular at least 90 wt % of the polyalkylene glycol bases.

The aromatic amine is of the formula (I)

wherein R1 and R2 are H or together represent the group A

and R3 and R4 are independently H or C₂-C₃₀ alkyl.

In one form of the aromatic amine R1 and R2 is H. In another form of the aromatic amine R1 and R2 together represent the group A.

R3 is usually in the 4-position of the phenyl ring.

In a preferred form R1 and R2 together represent the group A, R3 is H, and R4 is C₂-C₃₀ alkyl.

In another preferred form R1 and R2 are H, and R3 and R4 are independently C₂-C₃₀ alkyl.

Suitable R3 and R4 are independently H or n-propyl, isopropyl, n-, iso-, or tert.-butyl, n-pentyl, isoamyl, neopentyl, 2-ethylbutyl, n-hexyl, 1-methylpentyl, 1,3-dimethylbutyl, n-heptyl, isoheptyl, n-octyl, 1,4,4-trimethyl-2-pentyl, 3,4-, 3,5- or 4,5-dimethyl-1-hexyl, 3- or 5-methyl-1-heptyl, 1,1,3,3-tetramethylbutyl, 2-ethylhexyl, branched octyl, branched octyl as obtained from a dimer of isobutylene, n-nonyl, 1,1,3-trimethylhexyl, branched nonyl as obtained from a trimer of tripropylene, 1-methylundecyl, 2-n-butyl-n-octyl, branched dodecyl obtained from a trimer of isobutylene or a tetramer of propylene, branched pentadecyl obtained from a pentamer of propylene, 2-n-hexyl-n-decyl or 2-n-octyl-n-dodecyl.

Preferably, R3 and R4 are independently H or C₈-C₁₈ alkyl or both C₈-C₁₈ alkyl.

In another preferred form R3 and R4 are independently H or branched C₈-C₁₈ alkyl or both branched C₈-C₁₈ alkyl.

In another preferred form R3 and R4 are independently H or branched octyl as obtained from a dimer of isobutylene, branched nonyl as obtained from a trimer of tripropylene, branched dodecyl obtained from a trimer of isobutylene or a tetramer of propylene, or branched pentadecyl obtained from a pentamer of propylene.

In a preferred form the aromatic amine is of the formula (Ia)

where R1, R2, R3 and R4 are as defined above.

The aromatic amine of the formula (I) are known and commercially available, e.g. Irganox® L06 or Irganox® L57 from BASF SE, Germany.

The lubricant may comprise 0.05-5 wt %, preferably 0.1-3 wt %, and in particular 0.5-1.0 wt % of the aromatic amine.

The thioether of the formula (II) is commercially available.

The lubricant may comprise 0.05-5 wt %, preferably 0.1-3 wt %, and in particular 0.5-1.0 wt % of the thioether of the formula (II).

The weight ratio between the thioether and the aromatic amine may be from 1.5:1 to 1:1.5, preferably from 2:1 to 1:2, and in particular from 5:1 to 1:5.

Lubricants usually refers to composition which are capable of reducing friction between surfaces (preferably metal surfaces), such as surfaces of mechanical devices. A mechanical device may be a mechanism consisting of a device that works on mechanical principles. Suitable mechanical device are bearings, gears, joints and guidance's. The mechanical device may be operated at temperatures in the range of −30 C to 80° C. Lubricants are usually specifically formulated for virtually every type of machine and manufacturing process. The type and concentration of base oils and/or lubricant additives used for these lubricants may be selected based on the requirements of the machinery or process being lubricated, the quality required by the builders and the users of the machinery, and the government regulation. Typically, each lubricant has a unique set of performance requirements. In addition to proper lubrication of the machine or process, these requirements may include maintenance of the quality of the lubricant itself, as well as the effect of the lubricant's use and disposal on energy use, the quality of the environment, and on the health of the user.

Typical lubricants are automotive lubricants (e.g. gasoline engine oils, diesel engine oils, gas engine oils, gas turbine oils, automatic transmission fluids, gear oils) and industrial lubricants (e.g. industrial gear oils, pneumatic tool lubricating oil, high temperature oil, gas compressor oil, hydraulic fluids, metalworking fluids).

Examples for lubricants are axel lubrication, medium and heavy duty engine oils, industrial engine oils, marine engine oils, automotive engine oils, crankshaft oils, compressor oils, refrigerator oils, hydrocarbon compressor oils, very low-temperature lubricating oils and fats, high temperature lubricating oils and fats, wire rope lubricants, textile machine oils, refrigerator oils, aviation and aerospace lubricants, aviation turbine oils, transmission oils, gas turbine oils, spindle oils, spin oils, traction fluids, transmission oils, plastic transmission oils, passenger car transmission oils, truck transmission oils, industrial transmission oils, industrial gear oils, insulating oils, instrument oils, brake fluids, transmission liquids, shock absorber oils, heat distribution medium oils, transformer oils, fats, chain oils, minimum quantity lubricants for metalworking operations, oil to the warm and cold working, oil for water-based metalworking liquids, oil for neat oil metalworking fluids, oil for semi-synthetic metalworking fluids, oil for synthetic metalworking fluids, drilling detergents for the soil exploration, hydraulic oils, in biodegradable lubricants or lubricating greases or waxes, chain saw oils, release agents, molding fluids, gun, pistol and rifle lubricants or watch lubricants and food grade approved lubricants.

The lubricant has usually may have a kinematic viscosity at 40° C. of at least 10, 50, 100, 150, 200, 300, 400, 500, 600, 900, 1400, or 2000 mm²/s. In another form the lubricant has usually may have a kinematic viscosity at 40° C. from 200 to 10 000 mm²/s (cSt), preferably from 500 to 3 000 mm²/s, and in particular from 1000 to 1500 mm²/s.

The lubricant has usually may have a kinematic viscosity at 100° C. of at least 2, 3, 5, 10, 20, 30, 40, or 50 mm²/s. In another form the lubricant may have a kinematic viscosity at 100° C. from 10 to 5000 mm²/s (cSt), preferably from 30 to 3000 mm²/s, and in particular from 50 to 2000 mm²/s. The lubricant may have a viscosity index of at least 50, 75, 100, 120, 140, 150, 160, 170, 180, 190 or 200.

The lubricant is usually a lubricating liquid, lubricating oil or lubricating grease.

The lubricant usually further comprises

-   -   a further base oil in addition to the polyalkylene glycol         basestock selected from mineral oils, polyalphaolefins,         polymerized and interpolymerized olefins, alkyl naphthalenes,         alkylene oxide polymers, silicone oils, phosphate ester and         carboxylic acid ester; and/or     -   a lubricant additive.

The lubricant usually contains up to 10 wt %, preferably up to 5 wt %, and in particular up to 1 wt % of the further base oil. In another form the lubricant is free of the further base oil.

The further base oil may selected from the group consisting of mineral oils (Group I, II or III oils), polyalphaolefins (Group IV oils), polymerized and interpolymerized olefins, alkyl naphthalenes, alkylene oxide polymers, silicone oils, phosphate esters and carboxylic acid esters (Group V oils). Preferably, the base oil is selected from Group I, Group II, Group III base oils according to the definition of the API, or mixtures thereof. Definitions for the base oils are the same as those found in the American Petroleum Institute (API) publication “Engine Oil Licensing and Certification System”, Industry Services Department, Fourteenth Edition, December 1996, Addendum 1, December 1998. Said publication categorizes base oils as follows:

-   a) Group I base oils contain less than 90 percent saturates (ASTM     D 2007) and/or greater than 0.03 percent sulfur (ASTM D 2622) and     have a viscosity index (ASTM D 2270) greater than or equal to 80 and     less than 120. -   b) Group II base oils contain greater than or equal to 90 percent     saturates and less than or equal to 0.03 percent sulfur and have a     viscosity index greater than or equal to 80 and less than 120. -   c) Group III base oils contain greater than or equal to 90 percent     saturates and less than or equal to 0.03 percent sulfur and have a     viscosity index greater than or equal to 120. -   d) Group IV base oils contain polyalphaolefins. Polyalphaolefins     (PAO) include known PAO materials which typically comprise     relatively low molecular weight hydrogenated polymers or oligomers     of alphaolefins which include but are not limited to C2 to about C32     alphaolefins with the C8 to about C16 alphaolefins, such as     1-octene, 1-decene, 1-dodecene and the like being preferred. The     preferred polyalphaolefins are poly-1-octene, poly-1-decene, and     poly-1-dodecene. -   e) Group V base oils contain any base oils not described by Groups I     to IV. Examples of Group V base oils include alkyl naphthalenes,     alkylene oxide polymers, silicone oils, and phosphate esters.

Synthetic base oils include hydrocarbon oils and halo-substituted hydrocarbon oils such as polymerized and interpolymerized olefins (e.g., polypropylenes, propylene-isobutylene copolymers, chlorinated polybutylenes, poly(1-hexenes), poly(1-octenes), poly(1-decenes)); alkylbenzenes (e.g., dodecylbenzenes, tetradecylbenzenes, dinonylbenzenes, di(2-ethylhexyl)benzenes); poly-phenyls (e.g., biphenyls, terphenyls, alkylated polyphenols); and alkylated diphenyl ethers and alkylated diphenyl sulfides and derivative, analogs and homologs thereof.

Alkylene oxide polymers and interpolymers and derivatives thereof where the terminal hydroxyl groups have been modified by esterification, etherification, etc., constitute another class of known synthetic base oils. These are exemplified by polyoxyalkylene polymers prepared by polymerization of ethylene oxide and/or propylene oxide, and the alkyl and aryl ethers of polyoxyalkylene polymers (e.g., methyl-polyisopropylene glycol ether having a molecular weight of 1000 or diphenyl ether of polyethylene glycol having a molecular weight of 1000 to 1500); and mono- and polycar-boxylic esters thereof, for example, the acetic acid esters, mixed C3-C8 fatty acid esters and C13 oxo acid diester of tetraethylene glycol.

Silicon-based oils such as the polyalkyl-, polyaryl-, polyalkoxy- or polyaryloxysilicone oils and sili-cate oils comprise another useful class of synthetic base oils; such base oils include tetraethyl silicate, tetraisopropyl silicate, tetra-(2-ethylhexyl)silicate, tetra-(4-methyl-2-ethylhexyl) silicate, tetra-(p-tert-butyl-phenyl) silicate, hexa-(4-methyl-2-ethylhexyl)disiloxane, poly(methyl) siloxanes and poly(methylphenyl)siloxanes. Other synthetic base oils include liquid esters of phosphorous-containing acids (e.g., tricresyl phosphate, trioctyl phosphate, diethyl ester of decylphosphonic acid) and polymeric tetrahydrofurans.

Suitable lubricant additives may be selected from viscosity index improvers, polymeric thickeners, corrosion inhibitors, detergents, dispersants, anti-foam agents, dyes, wear protection additives, extreme pressure additives (EP additives), anti-wear additives (AW additives), friction modifiers, metal deactivators, pour point depressants.

The viscosity index improvers include high molecular weight polymers that increase the relative viscosity of an oil at high temperatures more than they do at low temperatures. Viscosity index improvers include polyacrylates, polymethacrylates, alkylmethacrylates, vinylpyrrolidone/methacrylate copolymers, poly vinylpyrrolidones, polybutenes, olefin copolymers such as an ethylene-propylene copolymer or a styrene-butadiene copolymer or polyalkene such as PIB, styrene/acrylate copolymers and polyethers, and combinations thereof. The most common VI improvers are methacrylate polymers and copolymers, acrylate polymers, olefin polymers and copolymers, and styrenebutadiene copolymers. Other examples of the viscosity index improver include polymethacrylate, polyisobutylene, alpha-olefin polymers, alpha-olefin copolymers (e.g., an ethylenepropylene copolymer), polyalkylstyrene, phenol condensates, naphthalene condensates, a styrenebutadiene copolymer and the like. Of these, polymethacrylate having a number average molecular weight of 10000 to 300000, and alpha-olefin polymers or alpha-olefin copolymers having a number average molecular weight of 1000 to 30000, particularly ethylene-alpha-olefin copolymers having a number average molecular weight of 1000 to 10000 are preferred. The viscosity index increasing agents can be added and used individually or in the form of mixtures, conveniently in an amount within the range of from ≥ 0.05 to ≤20.0% by weight, in relation to the weight of the base stock.

Suitable (polymeric) thickeners include, but are not limited to, polyisobutenes (PIB), oligomeric co-polymers (OCPs), polymethacrylates (PMAs), copolymers of styrene and butadiene, or high viscosity esters (complex esters).

Corrosion inhibitors may include various oxygen-, nitrogen-, sulfur-, and phosphorus-containing materials, and may include metal-containing compounds (salts, organometallics, etc.) and nonmetal-containing or ashless materials. Corrosion inhibitors may include, but are not limited to, additive types such as, for example, hydrocarbyl-, aryl-, alkyl-, arylalkyl-, and alkylaryl-versions of detergents (neutral, overbased), sulfonates, phenates, salicylates, alcoholates, carboxylates, salixarates, phosphites, phosphates, thiophosphates, amines, amine salts, amine phosphoric acid salts, amine sulfonic acid salts, alkoxylated amines, etheramines, polyether-amines, amides, imides, azoles, diazoles, triazoles, benzotriazoles, benzothiadoles, mercapto-benzothiazoles, tolyltriazoles (TTZ-type), heterocyclic amines, heterocyclic sulfides, thiazoles, thiadiazoles, mercaptothiadiazoles, dimercaptothiadiazoles (DMTD-type), imidazoles, benzimidazoles, dithiobenzimidazoles, imidazolines, oxazolines, Mannich reactions products, glycidyl ethers, anhydrides, carbamates, thiocarbamates, dithiocarbamates, polyglycols, etc., or mixtures thereof.

Detergents include cleaning agents that adhere to dirt particles, preventing them from attaching to critical surfaces. Detergents may also adhere to the metal surface itself to keep it clean and prevent corrosion from occurring. Detergents include calcium alkylsalicylates, calcium alkyl-phenates and calcium alkarylsulfonates with alternate metal ions used such as magnesium, barium, or sodium. Examples of the cleaning and dispersing agents which can be used include metal-based detergents such as the neutral and basic alkaline earth metal sulphonates, alkaline earth metal phenates and alkaline earth metal salicylates alkenylsuccinimide and alkenylsuccinimide esters and their borohydrides, phenates, salienius complex detergents and ashless dispersing agents which have been modified with sulphur compounds. These agents can be added and used individually or in the form of mixtures, conveniently in an amount within the range of from ≥0.01 to ≤1.0% by weight in relation to the weight of the base stock; these can also be high total base number (TBN), low TBN, or mixtures of high/low TBN.

Dispersants are lubricant additives that help to prevent sludge, varnish and other deposits from forming on critical surfaces. The dispersant may be a succinimide dispersant (for example N-substituted long chain alkenyl succinimides), a Mannich dispersant, an ester-containing dispersant, a condensation product of a fatty hydrocarbyl monocarboxylic acylating agent with an amine or ammonia, an alkyl amino phenol dispersant, a hydrocarbyl-amine dispersant, a polyether dispersant or a polyetheramine dispersant. In one embodiment, the succinimide dispersant includes a polyisobutylene-substituted succinimide, wherein the polyisobutylene from which the dispersant is derived may have a number average molecular weight of about 400 to about 5000, or of about 950 to about 1600. In one embodiment, the dispersant includes a borated dispersant. Typically, the borated dispersant includes a succinimide dispersant including a polyisobutylene succinimide, wherein the polyisobutylene from which the dispersant is derived may have a number average molecular weight of about 400 to about 5000. Borated dispersants are described in more detail above within the extreme pressure agent description.

Anti-foam agents may be selected from silicones, polyacrylates, and the like. The amount of anti-foam agent in the lubricant compositions described herein may range from ≥0.001 wt.-% to ≤0.1 wt.-% based on the total weight of the formulation. As a further example, an anti-foam agent may be present in an amount from about 0.004 wt.-% to about 0.008 wt.-%.

Suitable extreme pressure agent is a sulfur-containing compound. In one embodiment, the sulfur-containing compound may be a sulfurised olefin, a polysulfide, or mixtures thereof.

Examples of the sulfurised olefin include a sulfurised olefin derived from propylene, isobutylene, pentene; an organic sulfide and/or polysulfide including benzyldisulfide; bis-(chlorobenzyl) disulfide; dibutyl tetrasulfide; di-tertiary butyl polysulfide; and sulfurised methyl ester of oleic acid, a sulfurised alkylphenol, a sulfurised dipentene, a sulfurised terpene, a sulfurised Diels-Alder adduct, an alkyl sulphenyl N′N-dialkyl dithiocarbamates; or mixtures thereof. In one embodiment, the sulfurised olefin includes a sulfurised olefin derived from propylene, isobutylene, pentene or mixtures thereof. In one embodiment the extreme pressure additive sulfur-containing compound includes a dimercaptothiadiazole or derivative, or mixtures thereof. Examples of the dimercaptothiadiazole include compounds such as 2,5-dimercapto-1,3,4-thiadiazole or a hydrocarbyl-substituted 2,5-dimercapto-1,3,4-thiadiazole, or oligomers thereof. The oligomers of hydrocarbyl-substituted 2,5-dimercapto-1,3,4-thiadiazole typically form by forming a sulfur-sulfur bond between 2,5-dimercapto-1,3,4-thiadiazole units to form derivatives or oligomers of two or more of said thiadiazole units. Suitable 2,5-dimercapto-1,3,4-thiadiazole derived compounds include for example 2,5-bis(tert-nonyldithio)-1,3,4-thiadiazole or 2-tert-nonyldithio-5-mercapto-1,3,4-thiadiazole. The number of carbon atoms on the hydrocarbyl substituents of the hydrocarbyl-substituted 2,5-dimercapto-1,3,4-thiadiazole typically include 1 to 30, or 2 to 20, or 3 to 16. Extreme pressure additives include compounds containing boron and/or sulfur and/or phosphorus. The extreme pressure agent may be present in the lubricant compositions at 0 wt.-% to about 20 wt.-%, or at about 0.05 wt.-% to about 10.0 wt.-%, or at about 0.1 wt.-% to about 8 wt.-% of the lubricant composition.

Examples of anti-wear additives include organo borates, organo phosphites such as didodecyl phosphite, organic sulfur-containing compounds such as sulfurized sperm oil or sulfurized terpenes, zinc dialkyl dithiophosphates, zinc diaryl dithiophosphates, phosphosulfurized hydrocarbons and any combinations thereof.

Friction modifiers may include metal-containing compounds or materials as well as ashless compounds or materials, or mixtures thereof. Metal-containing friction modifiers include metal salts or metal-ligand complexes where the metals may include alkali, alkaline earth, or transition group metals. Such metal-containing friction modifiers may also have low-ash characteristics. Transition metals may include Mo, Sb, Sn, Fe, Cu, Zn, and others. Ligands may include hydrocarbyl derivative of alcohols, polyols, glycerols, partial ester glycerols, thiols, carboxylates, carbamates, thiocarbamates, dithiocarbamates, phosphates, thiophosphates, dithiophosphates, amides, imides, amines, thiazoles, thiadiazoles, dithiazoles, diazoles, triazoles, and other polar molecular functional groups containing effective amounts of O, N, S, or P, individually or in combination. In particular, Mo-containing compounds can be particularly effective such as for example Mo-dithiocarbamates, Mo(DTC), Mo-dithiophosphates, Mo(DTP), Mo-amines, Mo (Am), Mo-alcoholates, Mo-alcohol-amides, and the like.

Ashless friction modifiers may also include lubricant materials that contain effective amounts of polar groups, for example, hydroxyl-containing hydrocarbyl base oils, glycerides, partial glycerides, glyceride derivatives, and the like. Polar groups in friction modifiers may include hydrocarbyl groups containing effective amounts of O, N, S, or P, individually or in combination. Other friction modifiers that may be particularly effective include, for example, salts (both ash-containing and ashless derivatives) of fatty acids, fatty alcohols, fatty amides, fatty esters, hydroxyl-containing carboxylates, and comparable synthetic long-chain hydrocarbyl acids, alcohols, amides, esters, hydroxy carboxylates, and the like. In some instances, fatty organic acids, fatty amines, and sulfurized fatty acids may be used as suitable friction modifiers. Examples of friction modifiers include fatty acid esters and amides, organo molybdenum compounds, molybdenum dialkylthiocarbamates and molybdenum dialkyl dithiophosphates.

Suitable metal deactivators include benzotriazoles and derivatives thereof, for example 4- or 5-alkylbenzotriazoles (e.g. triazole) and derivatives thereof, 4,5,6,7-tetrahydrobenzotriazole and 5,5′-methylenebisbenzotriazole; Mannich bases of benzotriazole or triazole, e.g. 1-[bis(2-ethylhexyl) aminomethyl) triazole and 1-[bis(2-ethylhexyl) aminomethyl)benzotriazole; and alkoxy-alkylbenzotriazoles such as 1-(nonyloxymethyl)benzotriazole, 1-(1-butoxyethyl) benzotriazole and 1-(1-cyclohexyloxybutyl) triazole, and combinations thereof. Additional non-limiting examples of the one or more metal deactivators include 1,2,4-triazoles and derivatives thereof, for example 3-alkyl(or aryl)-1, 2,4-triazoles, and Mannich bases of 1,2,4-triazoles, such as 1-[bis(2-ethylhexyl) aminomethy1-1, 2,4-triazole; alkoxyalky1-1, 2,4-triazoles such as 1-(1-butoxyethyl)-1, 2,4-triazole; and acylated 3-amino-1, 2,4-triazoles, imidazole derivatives, for example 4,4′-methylenebis(2-undecyl-5-methylimidazole) and bis[(N-methyl)imidazol-2-yl]carbinol octyl ether, and combinations thereof. Further non-limiting examples of the one or more metal deactivators include sulfur-containing heterocyclic compounds, for example 2-mercaptobenzothiazole, 2,5-dimercapto-1, 3,4-thia-diazole and derivatives thereof; and 3,5-bis[di(2-ethylhexyl) aminomethyl]-1, 3,4-thiadiazolin-2-one, and combinations thereof. Even further non-limiting examples of the one or more metal deactivators include amino compounds, for example salicylidenepropylenediamine, salicylami-noguanidine and salts thereof, and combinations thereof. The one or more metal deactivators are not particularly limited in amount in the composition but are typically present in an amount of from about 0.01 to about 0.1, from about 0.05 to about 0.01, or from about 0.07 to about 0.1, wt.-% based on the weight of the composition. Alternatively, the one or more metal deactivators may be present in amounts of less than about 0.1, of less than about 0.7, or less than about 0.5, wt.-% based on the weight of the composition.

Pour point depressants (PPD) include polymethacrylates, alkylated naphthalene derivatives, and combinations thereof. Commonly used additives such as alkylaromatic polymers and polymethacrylates are also useful for this purpose. Typically, the treat rates range from ≥0.001 wt.-% to ≤1.0 wt.-%, in relation to the weight of the base stock.

Demulsifiers include trialkyl phosphates, and various polymers and copolymers of ethylene glycol, ethylene oxide, propylene oxide, or mixtures thereof.

EXAMPLES

-   PAG Basestock: random ethoxylated and propoxylated butanol, 50 wt-%     ethylene oxide units, Mn about 1200 g/mol (based on OH number), KV40     about 50 mm²/s, KV100 about 10 mm²/s. -   Amine Antioxidant A: aromatic amine of the formula (I), where R1 and     R2 are H, and R3 and R4 comprise independently branched octyl,     included in CAS [68411-46-1]. -   Amine Antioxidant B: aromatic amine of the formula (I), where R1 and     R2 together represent the group A, R3 is H, and R4 is branched     octyl, CAS [51772-35-1]. -   Thioether Antioxidant: thioether of the formula (II).

Example 1

The lubricants samples (each 30 g) contained the PAG basestock and 0.75 wt % of the Thioether Antioxidant and the 0.75 wt % of the Amine Antioxidant as described in Table 1.

TABLE 1 Composition of lubricant (data in wt %) Lubricant A Lubricant B PAG Basestock 98.75  98.75  Amine Antioxidant A 0.75 — Amine Antioxidant B — 0.75 Thioether Antioxidant 0.75 0.75

Example 2

The lubricant samples (each 30 g) from example 1 were stored for several weeks at 150° C. in an open flask without stirring in the presence of a round copper blank (1 mm thick, 16 mm diameter, about 2 g). The KV40 was determined and the results summarized in Table 2. The KV40 before heating was set as 100%.

TABLE 2 Evaluation of the KV40 [%] on storage at 150° C. Weeks Lubricant A Lubricant B 0 101 101 2 105 103 4 103 98 8 106 104 10 102 102

The data showed, that there was only minor increase or decrease in viscosity due to 5 decomposition of the polyalkylene glycol basestock. 

1.-14. (canceled)
 15. A lubricant comprising a polyalkylene glycol basestock, an aromatic amine of the formula (I)

wherein R1 and R2 are H or together represent the group A

and R3 and R4 are independently H or C₂-C₃₀ alkyl, and a thioether of the formula (II)


16. The lubricant according to claim 15, comprising 0.05-5 wt % of the aromatic amine.
 17. The lubricant according to claim 16, comprising 0.5-1.0 wt % of the aromatic amine.
 18. The lubricant according to claim 15, comprising 0.05-5 wt % of the thioether.
 19. The lubricant according to claim 18, comprising 0.5-1.0 wt % of thioether.
 20. The lubricant according to claim 15, where the weight ratio between the thioether and the aromatic amine is from 1.5:1 to 1:1.5.
 21. The lubricant according to claim 20, where the weight ratio between the thioether and the aromatic amine is from 5:1 to 1:5.
 22. The lubricant according to claim 15, where the polyalkylene glycol basestock has a kinematic viscosity at 40° C. in the range from 10-300 mm²/s.
 23. The lubricant according to claim 15, where the polyalkylene glycol basestock is an ethoxylated and propoxylated C₁-C₂₀ alkanol or C₂-C₂₀ alkandiol.
 24. The lubricant according to claim 15, where the polyalkylene glycol basestock is an ethoxylated and propoxylated C₁-C₈ alkanol.
 25. The lubricant according to claim 15, where the polyalkylene glycol basestock is an alkoxylated alcohol with a number average molecular weight Mn in the range from 400 to 10 000 Da.
 26. The lubricant according to claim 15, where the polyalkylene glycol basestock is an alkoxylated alcohol with a number average molecular weight Mn in the range from 1000 to 1500 Da.
 27. The lubricant according to claim 23, where the alkoxylated alcohol contains 30 to 70 wt-% ethylene oxide units, and 70 to 30 wt-% of propylene oxide units.
 28. The lubricant according to claim 15, where R1 and R2 together represent the group A, R3 is H, and R4 is C₂-C₃₀ alkyl.
 29. The lubricant according to claim 15, where R1 and R2 are H, and R3 and R4 are independently C₂-C₃₀ alkyl.
 30. The lubricant according to claim 15, where R3 and R4 are independently H or n-propyl, isopropyl, n-, iso-, or tert-butyl, n-pentyl, isoamyl, neopentyl, 2-ethylbutyl, n-hexyl, 1-methylpentyl, 1,3-dimethylbutyl, n-heptyl, isoheptyl, n-octyl, 1,4,4-trimethyl-2-pentyl, 3,4-, 3,5- or 4,5-dimethyl-1-hexyl, 3- or 5-methyl-1-heptyl, 1,1,3,3-tetramethylbutyl, 2-ethylhexyl, branched octyl, branched octyl as obtained from a dimer of isobutylene, n-nonyl, 1,1,3-trimethylhexyl, branched nonyl as obtained from a trimer of tripropylene, 1-methylundecyl, 2-n-butyl-n-octyl, branched dodecyl obtained from a trimer of isobutylene or a tetramer of propylene, branched pentadecyl obtained from a pentamer of propylene, 2-n-hexyl-n-decyl or 2-n-octyl-n-dodecyl.
 31. A method for preparing the lubricant as defined in claim 15 comprising the step of contacting the polyalkylene glycol basestock, the aromatic amine of the formula (I), and the thioether of the formula (II).
 32. A method for reducing the oxidative degradation of the polyalkylene glycol basestock as defined in claim 15 comprising the step of contacting the polyalkylene glycol basestock, the aromatic amine of the formula (I), and the thioether of the formula (II). 